The proposed project during year 3 will be focused upon the question of how and when 125 I-hCG enters different subcellular compartments in developing follicular and functioning luteal cells. Using hypophysectiomized estrogen primed immature rats time-dependent migration of 125 I-hCG will be followed within the target cells so that the nature of hCG entry after its association with the receptors may be studied. To this end quantitative radioautographic techniques at electron microscopic level will be used. BIBLIOGRAPHIC REFERENCES: Han, S.S., Cho, M.I. and Midgley, A.R., Jr. 1977. Intracellular of fate of 125 I-HCG in preovulatory follicular cells. Anat. Rec. Abstract. In press. Midgley, A. R., Jr., Zeleznik, A. J., Richards, J. S. and Han, S. S. 1977. Gonadotropin and estradiol receptor and follicular development. In: Sadler, W. A. and Segal, S. J., eds. Advances in Fertility Regulation Through Basic Research. In press.